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Garden Hits & Myths: Gardeners embracing biochar trend in 2020

Author of the article:

Jim Hole

Publishing date:

January 2, 2020 • 2 minute read

A worker lays out biochar to dry in the sun. Biochar is ideal for capturing and retaining water, oxygen and nutrients, while providing an ideal home for a multitude of beneficial soil microbes.Michele Sibiloni/ AFP/Getty Images

So, what is biochar? Quite simply, the term biochar is derived from ‘bios’ (life) and ‘char’ (carbonized wood or charcoal). Biochar begins its life as woody plant fibre that is undergoes high temperature heating or ‘pyrolysis’ without combusting or burning the fibre. What remains is a nearly pure carbon ‘skeleton’ that retains its original, porous physical structure and is ideal for capturing and retaining water, oxygen and nutrients, while providing an ideal home for a multitude of beneficial soil microbes.

While biochar is new to the world of gardening, it has been around for well over 2,000 years. Indigenous peoples of the Amazon discovered how biochar could be incorporated into soils to improve both crop yield and quality. The Portuguese called it ‘terra preta de indio’ which translates as ‘Indians black earth’ because biochar transformed highly weathered pale and poor-quality soils into rich, black, productive soils.

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But while biochar is great for improving the physical and chemical composition of poor soils, is also a powerful tool in the battle against climate change. Essentially, biochar is permanently sequestered carbon because it is not a food source for soil organisms. In comparison, manures and composts are digested by microbes and carbon dioxide is released into the air. That’s not to say that manures and composts aren’t great for improving soil quality, because they are, but a relatively small fraction of their organic matter remains after a few years thanks to hungry soil microbes, whereas biochar is completely unpalatable.

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There are a couple of other great benefits of biochar. It both reduces nutrient loss and pesticide damage through misapplication thanks to its glue-like affinity for many soil nutrients and organic compounds.

What should you do?

For our own gardens, biochar is a bit expensive for widespread use in our garden soils. But as an additive in potting soils, biochar shows great potential. For indoor plants like cacti and succulents that enjoy a relatively dry root environment, biochar can be used as a complete replacement for conventional peatmoss-based soils. Outdoors, I’ve found that a blend of about 20 per cent biochar to 80 per cent conventional potting soil works great for most containerized plants. A few centimetres of biochar also looks great as ‘surface topper’ by providing a rich, black, and attractive surface layer in containers, and it is also rather inhospitable to those annoying tiny black flies called ‘fungus gnats.’

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Now, one caveat with using biochar is that there are a number of different types with different properties and the ‘feedstock’ has a tremendous impact on the quality of the resulting biochar. Feedstock is simply a term describing the material from which biochar was derived. Some feedstocks might be tree wood, straw, or even manure. I happen to love bamboo because of its consistency and great porous structure.

So, is biochar right for you? From an ecological perspective, I think the answer is a definitive yes. Besides, 2,000 years of success by the Indigenous peoples of the Amazon would seem to indicate that biochar is certainly worth a shot in 2020.

Jim Hole is the owner of Hole’s Greenhouses in St. Albert and a certified professional horticulturist with the American Society for Horticultural Science.

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